SITE INFORMATION AND CORRESPONDENCE

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Geweke Land Development and Marketing - 3 - 18 October 2010 16 S. Cherokee Lane • Lodi, San Joaquin County site. Liquid hydrogen peroxide was introduced to select wells three times between May 1998 and January 1999 into select wells, to increase dissolved oxygen levels. In a 6 June 2001 meeting, Regional Board staff and the consultant concluded that Bio had reduced soil contamination; however, Bio had no affect on groundwater, as concentrations were not declining to the levels needed for closure and rescission of CAO 93-701. On 27 June 2001, a revised Monitoring and Reporting Program was issued by the Regional Board Executive Officer, which ceased Bio constituents monitoring and reduced groundwater monitoring frequencies., The 24 May 2002 Cone Penetrometer Testing Report Addendum for soil and groundwater identified TPHg contamination down to 134' below ground surface (bgs) and benzene down to 75' bgs, and recommended installation of clustered monitoring wells to define vertical extent of contamination. An 18 July 2002 workplan was approved, and deep monitoring wells MW-15 through MW-19 were installed December 2002. In April 2004, three ozone injection wells (OW-1 through OW-3) were installed (Attachment 2). The approved ozone injection pilot study, conducted from October 2004 through March 2005, was deemed successful, and in September 2005, four additional ozone injection wells (OW-1 R, OW-4 through OW-6) were installed for the full scale onsite remediation. However, petroleum hydrocarbons concentrations in groundwater at offsite monitoring well MW-9 did not decline in response to ozone injection, due to MW-9's distance from the ozone injection wells. In-situ chemical oxidation (ISCO) was proposed in January 2007 for MW-9, and a 10 December 2008 workplan for an ISCO pilot study was approved; however, the lack of funding due to the State Board UST Cleanup Fund payment delays resulted in no implementation of ISCO at MW-9. Onsite ozone injection ceased in December 2006. However, groundwater concentrations began rising significantly onsite by February 2007 and offsite in MW-9 by May 2007. Ozone injection resumed in March 2007 and continued until December 2008, when a second rebound test was conducted. Since December 2008, groundwater concentrations have not rebounded significantly, and are showing a slow declining trend with seasonal concentration spikes in onsite MW-14and offsite MW-9. On 30 June 2009, maximum groundwater monitoring concentrations were TPHg, 3,300 ug/L (MW-9); ethylbenzene, 18 ug/L (MW-14); and xylenes, 92 ug/L (MW-14). Risk Assessment Investigations to date show the bulk of onsite soil contamination existed from 15' bgs down to 60' bgs, where the consultant determined residual soil contamination poses minimal risk to human health from direct exposure, and over 50' west of the used car lot offices. The 10 November 2009 Soil Vapor Investigation Report (SVI Report) compared soil vapor sample results from three sample locations between MW-9 and the adjacent Lodi Adult School with the San Francisco Bay Regional Water Quality Control Board Environmental Screening Levels (ESLs). All soil vapor results were non-detect at reporting limits below the ESLs, the SVI Report conclusions show no risk from vapor intrusion to the nearby Lodi Adult School, and when extrapolating the soil vapor results, no vapor intrusion risk exists onsite. The consultant determined that residual petroleum hydrocarbons in groundwater did not pose a significant threat to human health or the environment. Land use (commercial and school zone) is not expected to change in the foreseeable future.